{"id":"CVE-2026-47722","aliases":["GHSA-7hp6-g3pq-3pc3","GO-2026-5223"],"url":"https://o3.security/vulnerability/CVE-2026-47722","summary":"nebula-mesh: Host advanced overrides allow YAML injection into agent config.yml","details":"`internal/configgen/generator.go:86,108,119` interpolates the operator-supplied `ListenHost` and `TunDevice` fields raw into a `text/template` that produces the agent's `config.yml`. `internal/web/advanced.go:20-35` accepts both with only `strings.TrimSpace` — no character or shape validation.\n\n## Exploit\nAn operator (or attacker with any operator key, given the cross-tenant CRUD advisory) sets `adv_tun_device` to:\n\n```\nnebula0\nlighthouse:\n  am_lighthouse: true\n  hosts: [\"10.0.0.1\"]\n#\n```\n\nThe agent fetches the rendered config on its next signed poll. On config reload, it loads the injected YAML keys: the host self-promotes to lighthouse, attracts mesh traffic, or sets `am_relay: true` to be selected as a relay. The `ListenHost` field has the same shape.\n\n## Affected\nAll released versions prior to v0.3.2.\n\n## Threat model\n- **Today**: operator can compromise their own host's config (trivially allowed if they own the host, but they can also set lighthouse/relay flags that the operator-create form does NOT expose — privilege uplift within their own tenant).\n- **Combined with the critical /api/v1 authz advisory**: any operator key can mutate ANOTHER tenant's host overrides and inject YAML there.\n- **Post-fix of the authz advisory**: still relevant — the agent unconditionally trusts whatever config the server hands it, so any future operator-impersonation bug re-amplifies this.\n\n## Suggested fix\nTwo options, either acceptable:\n\n1. **Input validation** in `parseAdvancedFromForm` (`internal/web/advanced.go`):\n   - `ListenHost`: regex `^[A-Za-z0-9.:\\[\\]_-]+$` (IPv4/IPv6/hostname)\n   - `TunDevice`: regex `^[A-Za-z0-9_-]{1,15}$` (Linux IFNAMSIZ caps at 15)\n   Reject invalid input with a form-level error; do not write to the host row.\n\n2. **Safer marshalling**: switch `configgen/generator.go` to marshal a typed Go struct via `gopkg.in/yaml.v3` (which escapes correctly) instead of `text/template` string-concat. Larger change, but eliminates this entire injection class.\n\nOption 2 is preferable long-term. Option 1 is the quick fix.\n\nThe `unsafe_routes` advanced field is already `netip.Parse{Prefix,Addr}`-validated at `enroll.go:226-233` — apply the same validation discipline to the other advanced fields.","published":"2026-07-23T19:19:41.976Z","modified":"2026-10-21T02:58:16.288385804Z","cvss":null,"epss":{"score":0.00467,"percentile":0.38726,"asOf":"2026-09-02"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/juev/nebula-mesh","fixedVersion":"0.3.2"}],"fix":{"url":"https://github.com/forgekeep/nebula-mesh/commit/c1506f7344ab375a145a7449b193af3f19bb41ef","label":"forgekeep/nebula-mesh@c1506f7"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47722.json"},{"type":"ADVISORY","url":"https://github.com/forgekeep/nebula-mesh/security/advisories/GHSA-7hp6-g3pq-3pc3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47722"},{"type":"REPORT","url":"https://github.com/forgekeep/nebula-mesh/issues/126"},{"type":"FIX","url":"https://github.com/forgekeep/nebula-mesh/commit/c1506f7344ab375a145a7449b193af3f19bb41ef"},{"type":"WEB","url":"https://github.com/juev/nebula-mesh/security/advisories/GHSA-7hp6-g3pq-3pc3"},{"type":"PACKAGE","url":"https://github.com/juev/nebula-mesh"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:16.288385804Z"}}